1. Field of the Invention
The present invention relates to an optical transmitter and receiver module, and particular to an integrated optical transmitter/receiver module.
2. Description of the Related Art
Recently, image information communications have been increasingly more common and attempts to adopt optical cables for communications have been made. Among these attempts, the access system optical communication adopts light waves of a wavelength band centered around 1.39 xcexcm for bidirectional communications between a plurality of subscribers and transmitter stations and at the same time, light waves of a wavelength band centered around 1.55 xcexcm for distributing image information from a transmitter station to the subscribers. In this type of system, it is necessary to install a WDM (Wavelength Division Multiplexing) optical transmitter and receiver module on the subscribers side of the system.
In the optical transmitter and receiver module, a type of module that employs a dielectric multilayer filter, that is, a reflective wavelength de-multiplexer, has received attention since the module realizes isolation over a broad bandwidth (Japanese patent application kokai 8-190026). As shown in FIG. 1, in a prior art optical transmitter and receiver module, single mode wave-guides 2, 3, and 2xe2x80x2 each having a core contained in a cladding 12 made of quartz-based glass are formed on a silicon substrate 11. Near a position of intersection of wave-guides 2 and 3, there is disposed a groove 4 formed with a dicing saw and a dielectric multilayer filter 5 is disposed therein. The optical axis of the wave-guide 2xe2x80x2 formed opposite to the wave-guides 2 and 3 of the dielectric multilayer filter 5 is in alignment with the optical axis of the wave-guide 2.
In a planar light-wave circuit 30, an input/output single mode optical fiber 10A and an output single mode optical fiber 10B are fixedly inserted into a glass block 9. The glass block 9 is fixedly bonded to the end face of the circuit so that the optical axes of the input/output and output single mode optical fibers 10A and 10B are in alignment with the optical axes of the wave-guides 2 and 3 respectively. Wavelength-multiplexed beams of light of wavelength bands centered around 1.3 xcexcm and 1.55 xcexcm are launched from the input/output port into the wave-guide 2. The light beam of a wavelength band centered around 1.55 xcexcm is reflected at the dielectric multilayer filter 5 to be guided into the wave-guide 3 and then is coupled into the output single mode optical fiber 10B at the end of the wave-guide to be outputted. On the other hand, the light beam of a wavelength band centered around 1.3 xcexcm from the wave-guide 2 passes through the dielectric multilayer filter 5, i.e., the reflective wavelength multiplexer/de-multiplexer, and enters the wave-guide 2xe2x80x2. The wave-guide 2xe2x80x2 is divided into two at a Y branch 6 in which one of branching wave-guide is connected to a laser diode 7 and the other is a photo-diode 8. The laser diode 7 is used for transmitting signals generated from one receiver of the subscribers to the input/output single mode optical fiber 10A, whereas the photo-diode 8 is used for converting the received optical signals into electric signals. Beams of light of a wavelength band centered around 1.55 xcexcm are used, for example, for distributing multi-channel video signals from a transmitter station to the subscribers, while beams of light of a wavelength band centered around 1.3 xcexcm are used in bidirectional communications for transmitting various kinds of data signals.
As mentioned above, the optical transmitter and receiver module is a filter reflective WDM module that employs the PLC (Planer Light-wave Circuit) hybrid integration technique having the functions of transmitting and receiving light waves of 1.55 xcexcm and of receiving 1.3 xcexcm, and of multiplexing and de-multiplexing those waves, with the compatibility of low cost and practical service durability.
In the foregoing, there are projections and depressions on the side face of a groove 4 dug and formed with a dicing saw, and thus it is difficult to grind the groove side faces. Accordingly, groove formation and filter insertion require high accuracy in the construction of this optical transmitter and receiver module. Thus, with this optical transmitter and receiver module, two-wave multiplexing of 1.55 xcexcm and 1.31 xcexcm can be managed, however, the module cannot be employed for communications of higher multiplicity from the point of view of filter resolution and loss thereof. In addition, the transmitter laser diode is vulnerable to the return light, so that there is a fear of an adverse effect thereof. Moreover, a dielectric multilayer filter 5 is formed by alternately depositing plural layers of SiO2 and TiO2 on a polyimide film of a predetermined thickness so that the dielectric multilayer filter 5 transmits light waves of a wavelength band centered around 1.3 xcexcm and reflects a wavelength band centered around 1.55 xcexcm. In addition, the film of this dielectric multilayer filter is inserted into the groove and fixed with a silicone adhesive 13 and is subject to deterioration with age. Furthermore, there is a problem in that the projections and depressions of the side face of the groove, the adhesive agent, and the plastic film cause the beams of light passing therethrough a great deal of loss in the reflection and transmission.
In view of the foregoing, the present invention has been made in view of the problem mentioned above, and the object of the present invention is to provide an optical transmitter and receiver module with less optical loss.
The optical transmitter and receiver module according to the present invention is an optical transmitter and receiver module which de-multiplexes a superimposed optical signal into which at least a first and second wavelength band are superimposed, and receives and transmits an optical signal of the first wavelength band, said optical transmitter and receiver module comprising
an input/output wave-guide having an outer end portion and inner end portion for inputting superimposed optical signals,
a receiver portion for receiving optical signals of the first wavelength band,
an output wave-guide having an outer end portion and inner end portion for outputting optical signals of the second wavelength band,
a transmitter portion for transmitting the optical signals of the first wavelength band, and
a dispersing/converging optical system comprising a diffraction grating which de-multiplexes optical signals of the first wavelength band and second wavelength band from said superimposed optical signal launched from the inner end portion of said input/output wave-guide, converges the optical signal of the second wavelength band to the inner end portion of said output wave-guide and converges the optical signal of the first wavelength band to said receiver portion, and also converges the optical signal of the first wavelength band, launched from said transmitter portion to the inner end portion of said input/output wave-guide.
In the optical transmitter and receiver module of the present invention, said diffraction grating is a plane diffraction grating, there are provided collimator lenses on optical paths in front of the inner end portion of said input/output wave-guide in said dispersing/converging optical system, said receiver portion, inner end portion of said output wave-guide and said transmitter portion, the inner end portion of said input/output wave-guide, said receiver portion, the inner end portion of said output wave-guide, and said transmitter portion are disposed respectively, relative to an incidence normal of said plane diffraction grating at a point of incidence on the optical path of said input/output wave-guide, at angular positions which satisfy the following equations:
Sin xcex10+Sin xcex11=mxcex1/xcex9
Sin xcex10+Sin xcex12=mxcex2/xcex9
Sin xcex13+Sin xcex10=mxe2x80x2xcex1/xcex9
0 less than xcex10 less than 90
0 less than xcex11 less than 90
0 less than xcex12 less than 90
xcex10xe2x89xa0xcex11xe2x89xa0xcex12
xe2x88x9290 less than xcex13 less than 0
wherein xcex1 is a first wavelength band,
xcex2 is a second wavelength band,
xcex9 is a lattice constant of the plane diffraction grating,
xcex1 is an incident angle of the superimposed optical signal from the inner end portion of said input/output wave-guide,
xcex11 is a diffraction angle of the +1-order diffraction light of the optical signal of the first wavelength band to said receiver portion,
xcex12 is a diffraction angle of the +1-order diffraction light of the optical signal of the second wavelength band to the inner end portion of said output wave-guide,
xcex13 is an incident angle of the optical signal of the first wavelength band from said transmitter portion, and
m and mxe2x80x2 denote diffraction orders of integer with inverse signs having an absolute value.
In the optical transmitter and receiver module of the present invention, said diffraction grating is a depressed diffraction grating, and, in the module there are lying the inner end portion of said input/output wave-guide in said dispersing/converging optical system, said receiver portion, inner end portion of said output wave-guide, and said transmitter portion, on the Rowland having a curvature radius of said depressed diffraction grating as the diameter thereof, respectively.